Three new variants of the avian influenza type-A H7N9 virus
have been found this winter, spurred by transmission in poultry
and the incorporation of genetic material from another strain
called H9N2, scientists at the Shanghai Public Health Clinical
Center and Institutes of Biomedical Sciences said. The new
strains may be behind a surge of infections in Guangdong, the
southern province bordering Hong Kong.

So far, 178 people are known to have been infected with
H7N9 this year, 19 more than in 2013, according to a list of
confirmed cases kept by Internet message board FluTrackers. Each
case increases the risk of the virus becoming better suited to
humans, rather than birds, giving it the ability to spread
easily from person to person. Zhejiang and Guangdong provinces
and the Shanghai metropolitan area have been the worst affected
regions, the scientists wrote in a paper published in
Eurosurveillance yesterday.

“The rapidly increasing number of cases of A(H7N9) virus
infection in these three regions may raise concerns as to
whether there is an association between circulation of the new
A(H7N9) reassortment strains identified and accelerated
transmission of A(H7N9) virus in humans,” the scientists said.
“It is of the utmost importance to monitor the risk of a
potential pandemic initiated by various influenza virus
strains.”

Pandemic Hotspot

Even though H7N9 hasn’t mutated to become as contagious as
seasonal flu, strains that emerge in China are of special
interest to researchers. The 1957-58 Asian Flu and 1968-69 Hong
Kong Flu pandemics were first identified in the world’s most
populous nation, and an earlier bird flu strain known as H5N1 is
thought to have come from the southern province of Guangdong in
1996. Years later, a new seasonal flu was found in neighboring
Fujian and triggered explosive epidemics worldwide.

H7N9 has infected about 350 people, killing more than 70,
mostly in mainland China, according to FluTrackers.

The new reassortments generated by H7N9 and H9N2 strains
may produce variants that are more adaptive and have an
increased ability to cause disease in humans, according to the
Eurosurveillance report.

Pandemic Risk

“Our findings suggest there is a possible risk that a
pandemic could develop,” the authors said.

So far, there is no evidence of sustained human-to-human
transmission, the World Health Organization in Geneva said in a
Feb. 11 statement.

“Each new strain could be one that is better genetically
equipped to transmit form person to person,” Ian Mackay, an
associate professor of clinical virology at the University of
Queensland in Brisbane, said in an e-mail today. “Without
contemporary sequence analysis, such a strain could emerge from
among the ‘noise’ of human infection by less efficient strains,
to begin spreading rapidly and with pandemic potential.”

It’s impossible to predict whether such a virus with the
ability to spread worldwide would remain so deadly, killing
about one in five people known to have been sickened with it.

Yesterday’s research was based on a study of 72 genetic
sequences of a flu gene called PB1 analyzed from samples
collected in 11 Chinese provinces and cities since March 2013.

The authors didn’t show why changes in the PB1 gene might
be related to increased pandemic risk, said Masato Tashiro, a
director at Japan’s National Institute of Infectious Diseases in
Tokyo, who reviewed the Eurosurveillance report. Other genes may
contribute to the risk, he said.

‘Interesting, Important’

Still, the research is “interesting and important,”
Tashiro said today in an e-mail.

“The H7N9 virus has undergone many gene reassortments with
different domestic H9N2 viruses in poultry in different areas in
China,” he said, adding that it’s not clear when the genetic
reassortments occurred.

The increase in human cases during the Northern Hemisphere
winter may reflect a wider spread of the H7N9 virus in poultry.
The virus can circulate widely in chickens, ducks and geese
without causing the mass die-offs characteristic of the H5N1
bird flu virus. Its stealth has made it difficult to track and
contain a germ that’s typically more active during the colder
winter months, scientists said.

The initial wave of H7N9 cases last year occurred late in
the Northern winter and was limited to a smaller geographic
region compared with the second wave, which began in October and
was being fanned by a surge in poultry production timed for
lunar New Year feasts that began at the end of January. These
factors may facilitate greater genetic diversity of the
circulating H7N9 strains, the University of Queensland’s Mackay
said.

‘In the Dark’

“We do see minor genetic differences” in H7N9 samples,
said Ian Barr, deputy director of the WHO’s Collaborating Center
for Reference and Research on Influenza in Melbourne. “We’re
still in the dark a little about the significance of any minor
clades” or genetic variants.

“The epidemiological data doesn’t support the premise that
we have got either increased transmissibility or increased
pathogenicity with this current outbreak versus the one in early
2013,” Barr said in a telephone interview today.

Sequencing studies involving genes other than PB1 are
needed to get a better understanding of how the H7N9 strain is
evolving, Mackay said.

“We have yet to see similar examination of the rest of the
H7N9 genome in such detail,” he said. “That is urgently needed
to tell the experts what today’s H7N9 is potentially capable
of.”